Question

you may use the tables of slide #18 of module 4.1 to answer the following questions. (1) what is the number of formula units within the unit cell of nacl? select (2) what is the number of formula units within the unit cell of cscl? select (3) what is the number of formula units within the unit cell of sic? select

Explanation:

Step1: Recall NaCl unit - cell structure

In a face - centered cubic (FCC) unit cell of NaCl, the number of formula units can be calculated using the contribution of ions from different positions. Sodium ions ($Na^+$) and chloride ions ($Cl^-$) are arranged in an FCC - like structure. The number of $Na^+$ and $Cl^-$ ions in the unit cell is 4 each. So, the number of NaCl formula units in the unit cell is 4.

Step2: Recall CsCl unit - cell structure

In a CsCl unit cell, which has a simple cubic lattice structure for each of the ion types (Cs⁺ and Cl⁻), the unit cell contains 1 Cs⁺ ion at the center and 8 Cl⁻ ions at the corners (or vice - versa). The contribution of corner ions to the unit cell is $\frac{1}{8}$ each. So, the total number of formula units of CsCl in the unit cell is 1.

Step3: Recall SiC unit - cell structure

In a SiC unit cell, considering the tetrahedral bonding and the arrangement of Si and C atoms, the number of SiC formula units in the unit cell is 4.

Answer:

(1) 4
(2) 1
(3) 4